1. Field of the Invention
The present invention is directed to the novel use of a high temperature material in engine and exhaust system parts and a method of preventing fires resulting from exhaust system failure. More particularly, the invention is directed to engine and exhaust system parts and engine compartment parts for positive displacement engines, for example piston-driven engines.
2. Discussion of the Background
Aircraft safety is an important and critical aspect of modern aviation. Aircraft safety for both private aircraft and commercial aircraft is regulated by the Federal Aviation Administration (FAA). An important aspect of aircraft safety is the construction and maintenance of aircraft engine and exhaust system components in order to prevent engine fires and additional damage associated with engine fires. Aircraft fires of any type are a serious problem. Fires in the engine compartment and in the aft engine compartment cause particularly severe problems in aircraft in which the wing spar passes through or near the engine compartment. Engine fires occurring in such aircraft can result in failure of the wing spar and separation of the wing from the aircraft during flight.
In situations in which the wing spar does not collapse, engine compartment fires still represent a serious safety problem. A major cause of fire in the engine compartment is failure of engine or exhaust system components operating at high temperatures. Component failure is aggravated in engines where very hot exhaust gas is routed to additional engine components such as a turbocharger instead of being simply vented outside the engine compartment. In such situations, deterioration of engine and exhaust part can occur rapidly. Engine compartment fire is an extreme aircraft emergency for the following reasons.
1. The engine compartment contains many systems that can complicate a fire situation. These systems include the fuel, engine oil, hydraulic and electrical systems. The failure of a turbocharger exhaust assembly within the engine compartment allows extremely hot gases to directly contact and destroy the integrity of the systems contained in the engine compartment.
2. The standard pilot response to an engine fire includes the shutting down of the engine. The shutting down of an aircraft engine, even on a twin engine aircraft, creates a very serious engine-out situation in which the pilot must cope with a potentially underpowered aircraft, unbalanced thrust and additional drag factors. Loss of the engine in a single-engine plane can be a catastrophe. The loss of an engine contributes substantially to crashes based on the loss of the engine alone. The presence of an onboard engine fire greatly exacerbates this situation.
3. Engine fires have demonstrated the ability to freeze the engine controls so that the pilot cannot feather his engine. In this situation, the only way to shut off the engine is to cut off the magnetos and/or fuel selector switch. After the engine has been shut down, the prop will windmill thereby increasing drag and continue to pump oil out of any ruptured oil lines. Aircraft with lower power ranges are frequently unable to maintain altitude with a windmilling engine.
4. In some aircraft, a single engine runs the hydraulic system pump, although some planes are equipped with auxiliary electrical hydraulic pumps. A pilot under the stress of an engine fire may shut down the engine running the hydraulic system pump thereby losing hydraulic pressure necessary to operate the control surfaces of the aircraft. Landing gear will frequently lower under such circumstances due to the fail-safe design of such systems. Lack of control surfaces combined with the increased drag of a windmilling engine and lowered landing gear contribute to aircraft instability.
6. In twin engine aircraft, the wing spar is located in the aft engine compartment and contains fuel and oil lines. Fires in the engine compartment cause the firewall to fail, ultimately resulting in rupture of the oil and fuel lines.
7. Smoke caused by the fire can enter the aircraft cabin of pressurized twin aircraft by way of the engine through the bleed air system. Smoke in the engine compartment interferes with pilot vision further reducing aircraft safety and contributing to aircraft accidents.
In single engine aircraft, fire in the engine compartment may directly interfere with the pilot's vision. Alternatively, smoke from engine compartment fires can easily enter the cockpit interfering with pilot vision and aircraft control. Damage to oil lines resulting from engine compartment fire can result in oil leaks with the possibility of oil on the windshield further reducing pilot vision and safety. Although there is generally no danger to the wing spar from an engine compartment fire in single engine aircraft, such fires are serious and life threatening to the pilot.
The critical nature of aircraft engine fires and exhaust system fires have been recognized by the FAA which has issued regulations and airworthiness directives (AD's) in an attempt to address exhaust system failures and safety. See for example Federal Aviation Regulation 23.1121, 23.1123 and 23.1125. With regard to some smaller turbocharged piston-engine aircarft, emergency air worthiness directives have been issued requiring the installation of fire detection kits to provide early warning of engine and exhaust system fires. See FAA-AD 90-01-02. In addition to actions by governmental agencies, private aircraft owners associations have also expressed concern with regard to engine and exhaust system failures and have attempted to address these problems.
Private aircraft associations in cooperation with the FAA have studied aircarft engine fires. Fires have been attributed, for example, to cracks occurring in the engine and exhaust system components, brackets and clamps and the firewall as a result of vibration. Additional stress occurs from repeated heating and cooling cycles of the engine and exhaust parts which are typically very hot during operation of the engine. Vibration and thermal stress are thought to contribute significantly to cracks occurring in the manifold and tailpipe assemblies as well as cracks in the associated flanges and brackets which secure the manifold and tailpipe assemblies to the engine, firewall or engine compartment. Loosening of the manifold and tailpipe assemblies due to vibration and heat stress can result in separation of the exhaust system from the engine itself. In such an event, the hot exhaust gases are no longer directed out of the engine compartment but directly contact the firewall and other engine components.
Proposed solutions to the thermal and vibration problems include a redesign of the engine and exhaust systems using heavier gauge materials, more secure attachment methods, secondary clamps and brackets to provide redundant fastening means to an existing tailpipe assembly, the installation of fire resistant hoses behind the firewall to further protect oil and fuel lines, the elimination of fuel and oil pressure lines altogether with electric gauging systems, the addition of flame deflector chutes to the firewall area and the application of intumescent coatings to the firewall to further prevent fire.
None of the proposed solutions to the problem of engine compartment fires, proposed by the FAA or by private groups have so far eliminated the problem of engine compartment fires. None of these solution have identified a critical feature of engine compartment fires and current engine and exhaust system construction. Without recognition of critical flaws in engine and exhaust assembly components, a solution to the problem of engine compartment fires cannot be achieved.
Clearly, any engine fire in a vehicle is a critically dangerous problem. Aircraft engine fires resulting from exhaust system failure of positive displacement aircraft engines are a serious problem to both private and corporate aviation. Although potential sources of the fires have been evaluated and numerous suggestions have been advanced by both the FAA and private groups, a need continues to exist for improved engine and exhaust systems and a method preventing engine compartment fires.